1. Field of the Invention
The present invention relates to a toner to be used in a recording method utilizing an electrophotographic method or the like, and an image-forming method.
2. Description of the Related Art
Various electrophotographic methods have been known. A general electrophotographic method involves the utilization of a photoconductive substance, and includes: forming an electrostatic latent image on an electrostatic image bearing member (which may hereinafter be referred to as “photosensitive member”) by various means; developing the latent image with toner to provide a visible image; transferring the toner image onto a recording medium such as paper as required; and fixing the toner image on the recording medium with heat, pressure, or the like to provide a copied article. An image-forming apparatus which adopts such electrophotographic method is, for example, a copying machine or a printer. In recent years, such printer or copying machine has showed a shift from image formation in an analog fashion to image formation in a digital fashion, and hence has been strongly requested to have an additionally increased speed and an additionally reduced size as well as to show excellent reproducibility of a latent image and a high resolution.
Here, attention is paid to the reduction in size. A reduction in diameter of, for example, a latent image bearing member or toner carrying member in an image-forming step is an essential condition for the reduction in size. In addition, a reduction in diameter of the toner carrying member increases the number of times of contact between toner and a toner control member, whereby a uniform charge quantity is provided for the toner, and, at the same time, the toner carrying member is uniformly coated with the toner. As a result, an improvement in quality of an image formed with the toner can be expected.
However, the reduction in diameter of the latent image bearing member or toner carrying member means that the curvature of the bearing member or carrying member increases, and involves the emergence of the following detrimental effect: a developing zone becomes extremely narrow in a developing portion. Particularly in jumping development as magnetic, one-component development, a narrow developing zone causes the following problem: the amount of toner to be developed reduces, so a sufficient image density cannot be obtained.
In addition, the following phenomenon also known as “sweeping” is known to occur in the jumping development: an electric line of force orients toward a solid black edge portion in a boundary region between a solid black portion and a solid white portion, so the amount of toner with which the edge portion is developed increases. The phenomenon is known to occur at a site where a distance between an electrostatic latent image bearing member and a toner carrying member (hereinafter abbreviated as “S-D distance”) rapidly increases, that is, the rear end of a developing zone, and generally occurs remarkably when a toner carrying member or electrostatic latent image bearing member having a large curvature is used.
To cope with the phenomenon, it has been reported that sweeping can be alleviated by inserting a plate-like member into a developing zone (Japanese Patent Application Laid-Open No. 2005-077702 A). However, when a toner carrying member having a small diameter is used, the following problem is apt to arise: the insertion of the plate-like member into the developing zone additionally narrows the developing zone, with the result that an image to be formed hardly shows a high density.
Although a sufficient image density can be obtained by extending the developing zone by certain means, an abrupt increase in the S-D distance at the rear end portion of the developing zone occurs, so sweeping may be additionally remarkable.
As described above, there is a trade-off between an image density and sweeping when a toner carrying member having a small diameter is used.
Attempts have been made to alleviate those problems by controlling the flowability of magnetic toner. For example, the degree of agglomeration of the toner is adjusted (Japanese Patent Application Laid-Open No. 2003-43738 A), or the compressibility of the toner is controlled (Japanese Patent Application Laid-Open No. 2000-181128 A or Japanese Patent Application Laid-Open No. 2001-356516 A). Further, a toner having an adjusted contact angle with water has been proposed (Japanese Patent Application Laid-Open No. H04-067045 A or Japanese Patent Application Laid-Open No. 2000-047428 A), but is still susceptible to improvement in terms of an increase in density of an image formed with the toner and the alleviation of sweeping when the toner is combined with a toner carrying member having a small diameter.